Adjust descriptor count of storage buffers when compute shader is used

Adjust descriptor count of storage buffers when compute shader is used

A storage buffer descriptor is required for writing test results when compute
shader is used. Previously, one additional descriptor was being added to the
descriptor count in case of compute shader but that caused storage buffer
binding count to exceed device limits (maxPerStageDescriptorStorageBuffers).
Now, adjustment has been made to exclude one descriptor from descriptor count
test value when setting up descriptor sets in case of compute shader.

Affects:
dEQP-VK.pipeline.*.descriptor_limits.*

Components: Vulkan
VK-GL-CTS issue: 4330

Change-Id: I5b42d39207e6086a274b7cfaf9d66a346fd3aaf0